Acute maxillary sinusitis developed in three critically ill patients whose conditions required mechanical ventilation. In all three, fever was the initial clinical manifestation. An obtunded state and an inability to speak delayed localization of the site of infection. Prolonged intubation, simultaneous use of nasal gastric tubes, poor healing, and large-diameter endotracheal tubes likely contributed to the disease pathogenesis. Acute maxillary sinusitis may be the cause of unexplained fevers in patients with nasotracheal intubation.